Brihadaranyaka Upanishad
The true nature of the Self is to be free from fear, free from desire and free from evil.

As lovers in deep embrace forget everything and only feel peace all around, when a person embraces his true Self he feels peace all around. In that state of peace there is neither father nor mother, and there are no gods. He can neither, see, hear, taste, smell, know or feel. Yet he can see – for sight and he are one; he can hear – because sound and he are one; he can taste – for taste and he are one; he can smell – for he and smell are one; he knows – for he and knowledge are one; he can touch – for he and touch are one.

The Self is eternal and immortal, man’s highest goal and deepest bliss. Most creatures can only experience a small part of this bliss, so human beings are very lucky indeed.

When a person is about to die, the lower self groans, like a heavily laden cart. Then the Higher Self takes charge and prepares for the final journey. The dying person becomes weak and seemingly unconscious. His powers and senses unite with his subtle body. Then by the light of the Self, life departs from the body. But the Self remains conscious and with consciousness the dying man goes on his journey.
The deeds of his life and their results go with him.

Just as a caterpillar when it reaches the end of a blade of grass moves on to another blade and moves his body from the first, so the Self, having reached the end of this body, enters a new one. Or as a goldsmith takes an old vase, melts it down and reshapes it into a new one, so the Self after death eventually comes back in a new vessel, perhaps a human body, perhaps a celestial being.

We act according to our desires. After death we go to the next world bearing the subtle impressions of our prior deeds. We return with the same desires, and thus continue birth after birth.
However, when we have conquered desire, we do not return and are allowed to become one with the Supreme Reality. The path from desire to liberation is long and hard. It is only by treading this path that we can realize the Supreme Reality. Those who tread this path have no desire for children, wealth or power; evil is burned away and we are freed from desire, sorrow and doubt.

Brihadaranyaka Upanishad